A kind of star-shaped brain cell that helps support surrounding nerve cells plays a much more pivotal role in maintaining the brain's vitality than researchers had thought. According to a study in the current issue of Cell, astrocytes double as neural stem cells, the source of new nerve cells.
Neurobiologist Arturo Alvarez-Buylla of The Rockefeller University in New York City got interested in the adult mammalian brain's capacity to produce new cells after he and others discovered in the 1980s that songbirds renew large parts of their brains every year. In the current study, Alvarez-Buylla and Fiona Doetsch focused on mouse ventricles, a series of interconnected cavities in the brain. Underneath a layer of hairy cells that line these cavities, they found a region where new, slender nerve cells had formed. The fresh cells were encased in tunnels formed by appendages of cells that looked very much like astrocytes.
To track down the source of the new cells, Doetsch injected adult mouse brains with an anticancer compound that selectively kills rapidly dividing cells but leaves mature cells alone. "To our surprise, the whole region regenerated in 10 days," says Alvarez-Buylla. The team also created a mouse strain whose astrocytes carried a marker gene whose presence could be followed biochemically and with the electron microscope. Some of these cells lost their star shape and began to form new nerve cells in a brain region responsible for smell.
The finding marks an important step toward harnessing the body's rejuvenating powers for treating neurodegenerative diseases. "It's going to make [neurobiologists] look at these cells in more detail," says Susan Barnett, a neurobiologist at the University of Glasgow in the United Kingdom. "It will be interesting to see if they can be purified and used in [brain] repair."